Silurian

The Silurian is a time period in Earth's history that lasted for 23.5 million years, from 443.1 million years ago to 419.62 million years ago. It was the third and shortest period of the Paleozoic Era, part of the larger Phanerozoic Eon. Scientists know when this period began and ended by studying special layers of rock, but the exact dates are still being figured out.

One of the most exciting things that happened during the Silurian was the first time plants began to grow on land. These early vascular plants were different from simpler plants and marked a big change for life on Earth. At the same time, fungi and various small creatures like spiders, millipedes, and insects also started living on land.

The Silurian period also saw many new kinds of fish appear in the oceans. These included different types like placoderms, acanthodians, and bony fish. However, some older kinds of fish, like those without jaws, became much less common during this time.

History of study

The Silurian system was first identified by the Scottish geologist Roderick Murchison. He was looking at rocks with fossils in south Wales in the early 1830s. He named these rocks after a Celtic tribe in Wales called the Silures. This idea came from his friend Adam Sedgwick, who had named another time period the Cambrian after a Latin name for Wales.

In 1835, Murchison and Sedgwick shared a paper about the Silurian and Cambrian systems. This helped create the modern geological time scale. Later, another scientist named Charles Lapworth helped solve some disagreements by creating a new system called the Ordovician.

A French geologist named Joachim Barrande studied Silurian rocks in Bohemia and divided them into different stages. His work helped make Bohemia an important place for learning about early Silurian fossils.

Subdivisions

Paleogeography

During the Silurian time, a huge landmass called Gondwana sat near the equator, with a big ocean covering most of the north. The high water levels and flat lands created many island chains and many different environments.

Gondwana slowly moved toward the south, but there was less ice than before. As the ice melted, sea levels rose, covering older land layers. Three land areas—Avalonia, Baltica, and Laurentia—moved closer to the equator, beginning to form a new big landmass called Euramerica.

When early Europe bumped into North America, it pushed up lots of rocks, forming mountains from New York State through Europe and Greenland to Norway. By the end of this time, sea levels fell, leaving dry areas, and the new mountains wore down quickly. The big ocean Panthalassa covered most of the north, with some smaller oceans around.

Climate and sea level

The Silurian period used to be thought of as having steady, warm weather. But we now know the climate changed a lot during this time. The sea levels went up during the first half of the Silurian and then went down for the rest of it. There were fifteen times when the sea rose above the edge of the land.

The Earth was in a warm phase with lots of a gas called CO₂. Glaciers melted away near the South Pole. Layers of broken shells show that strong storms happened often because of the warm oceans.

Flora and fauna

The Silurian period was a time when life on land began to grow. Scientists think it was a recovery time after a big change in the world before this. During the Silurian, we started to see tiny forests made of moss-like plants and other simple plants along lakes and streams. This was the start of a big change called the Silurian-Devonian Terrestrial Revolution.

The first plants with special tissues that carry water and food appeared in the second half of the Silurian. One of the earliest known plants was Cooksonia. Most places where we find Cooksonia fossils are in the ocean, but they probably lived near rivers and streams. Another plant, Baragwanathia, had branching stems and needle-like leaves. Fossils of this plant have been found in Australia, Canada, and China.

We also know about some of the first animals that lived on land from the Silurian. The oldest known millipede, Kampecaris obanensis, lived in the late Silurian. There were also other small animals like centipedes and spider-like creatures. In the oceans, the first bony fish appeared. These fish had bony scales and could move their jaws. Sea scorpions, called eurypterids, swam in the shallow seas and lakes. Many different kinds of sea creatures lived during this time, including brachiopods, bryozoans, bivalves, chitons, and trilobites. Corals and other reef animals also began to appear and grow in some places.